Beryllium is produced commercially in the United States principally by two processes depending on whether the ore processed contains a soft or hard mineral. Soft mineral-containing ores, such as bertrandite (4BeO.2SiO.sub.2.H.sub.2 O ), although not capable of being concentrated by flotation if large amounts of clay are present, are directly leachable with sulfuric acid at about 95.degree. C. Calcium carbonate and calcium fluoride clays in the ore will consume acid to form gypsum which is discarded with the waste ore. The beryllium sulfate leach solution is separated from waste solids by thickeners to provide a leachate dilute in beryllium (about 0.1-0.2 wt % as BeO). The separated leach solution is solvent-extracted with bis(di-2-ethylhexyl) phosphoric acid (DEHPA) into kerosene. After stripping the organic phase, the solution is heated to precipitate iron and aluminum as hydroxide or basic carbonate. Further heating to 95.degree. C. precipitates basic beryllium carbonate and continued heating at about 165.degree. C. produces beryllium hydroxide.
Beryllium is produced from hard ores containing minerals such as beryl (3BeO Al.sub.2 O.sub.3 6SiO.sub.2) or phenacite (2BeO SiO.sub.2) by melting an ore concentrate containing at least 10% beryllium as BeO at 1600.degree.-1700.degree. C., quenching in water to produce a glassy frit, heat-treating the frit at 1000.degree. C., milling to a powder, mixing the powder with concentrated sulfuric acid, and baking at 325.degree. C. to form a beryllium sulfate solution containing about 3.0% beryllium as BeO. About 95% of the beryllium is leached with water. The leachate is extracted into DEHPA in kerosene, and the organic phase stripped with sodium or ammonium hydroxide before stagewise hydrolysis to recover solid beryllium hydroxide. Considerable care must be taken to avoid formation of gelatinous SiO.sub.2 in the water leaching step because of the difficulty of separating gelatinous material.
In one commercial process, dilute acidic beryllium sulfate leachates from soft and hard minerals are combined for the solvent extraction, stripping and hydrolysis steps to yield beryllium hydroxide. Since the combined leachate feed to solvent extraction is very dilute, processing equipment must be large and substantial amounts of raffinate waste must be purged. However, if the extraction feed were concentrated in order to reduce volume, the rate of extraction would be lowered due to increased acidity.
High temperature processes wherein beryl ores are fluorinated and water-leached or are fused with and without lime followed by cooling and sulfuric acid leaching, have been extensively investigated, reported and compared as in Everest, D. A., et al., "Economic Assessment of Four Processes for the Production of Beryllium Hydroxide from Flotation Concentrates", Trans. Inst. Min. Metall., 74 (13), 1964.
Milder reaction conditions for recovering beryllium from its ore, such as direct alkali leaching, have been reported. U.S. Pat. No. 3,615,260 describes the leaching of a beryllium ore with a 20-40 wt % caustic solution at 100.degree.-200.degree. C. for about 20 minutes, separating the waste solids from the high caustic leachate, and then adding lime or lime hydrate to precipitate silica but not beryllium. The product liquor is very dilute in beryllium and the beryllium is precipitated only upon further dilution and addition of lime. About 95% of the beryllium is coprecipitated with calcium hydroxide and silicates. Since the lime is added after the caustic leaching, the dissolved silica apparently lowers the equilibrium beryllium solubility such that the beryllium cannot be precipitated directly from solution. Based on the relatively mild reaction conditions of the patent, the beryllium ore treated probably contained a soft mineral such as bertrandite.
U.S. Pat. No. 2,298,800 describes a concentrated caustic leaching process for recovering beryllium from the hard minerals beryl or phenacite. The resulting slurry is diluted with water to precipitate dissolved beryllium hydroxide along with all of the waste ore. These solids are separated from the liquor and mixed again with circulating sodium carbonate/bicarbonate solution to dissolve the beryllium. After separating the waste ore from the dissolved beryllium, the solution is digested, beryllium hydroxide is precipitated and CO.sub.2 is evolved. The liquor from the precipitation is recontacted with CO.sub.2 and recycled to dissolve more beryllium from the caustic-decomposed ore. Additional CO.sub.2 is required since residual caustic in the leached wet ore cake is neutralized by the bicarbonate when dissolving the beryllium. This process thus requires two solvents in order to produce a solution from which beryllium hydroxide can be precipitated and the lime addition is only after the caustic leach.
As discussed by A. R. Burkin, Proceedings of the 1960 International Minerals Processing Congress, Warminster, England, when a beryl ore is leached with caustic the beryllium will re-precipitate as an amorphous solid when the silica concentration becomes too high, thereby essentially shutting down the leaching operation. Apparently for this reason commercial processes have resorted to acid leaching of an alkaline fused, or partially leached, silicate-based beryllium ore such as beryl, bertrandite and phenacite.
It will be evident that the known processes for producing beryllium from its ores are limited by the nature of the ore, i.e., whether it contains a hard or soft mineral, or the processes to be effective require extraordinary provisions for dealing with problems occasioned by acid leaching, such as preventing the formation of gelatinous silicates, or the processes require high temperature roasting or fusion, resulting in high energy costs and increased risk of exposure to toxic particulates. Beryllium compounds are highly toxic, one governmental regulation limiting beryllium in air emissions to 2 micrograms per cubic meter. From the standpoint of toxicity alone, therefore, a hydrometallurgical process such as a caustic leach is highly desirable. Nevertheless, the only known caustic leach processes have not been efficient due primarily to the presence of silica in the ore either as free silica or as the bound silica present in virtually all beryllium minerals.